Canine flank alopecia

CANINE FLANK ALOPECIA IS THE PREFERRED TERM for this disorder as it may occur at different times of the year, vary in the time and duration that dogs are affected, be continuous or sporadic and also vary according to the latitude where the dog resides (Miller and others, 2013).

The cause is unknown, but changes in the duration of light exposure appear to be important and melatonin secretion from the pineal gland may be involved.

Clinical features

• The age of onset is between one and 11 years, although most cases occur between three and six years (Miller and others, 2013), with a mean of 3.8 years.
• There is a breed predilection for the Boxer, but other breeds at risk include Airedale terrier, English bulldog, all sizes of Schnauzers, and many other breeds less commonly. There is no sex predilection, entire or neutered.
• The onset in northern hemispheres is typically between November and March with the development of a non-inflammatory, well-demarcated alopecia affecting the flank. This tends to be (but not always) bilaterally symmetrical, and the symmetry is often not identical. Occasionally the axilla, dorsum and bridge of the nose are affected. Hyperpigmentation commonly develops and rarely secondary infection.
• Many affected dogs re-grow hair three to eight months later. The new hair may be dull, dry and patchy.
• The disease is unpredictable and cannot be forecast for any particular dog. According to one authority (Paradis, 2000) 20%  have one episode with no recurrence. Other dogs have regular cyclic episodes at the same time each year, others may miss an episode in a particular year, while in a further group of dogs the alopecia develops permanently.
• Affected dogs are otherwise well.

Differential diagnosis

(from Hnilica, 2013)

• Superficial pyoderma. Cytology will demonstrate the presence of pyoderma but appropriate antimicrobial therapy will not improve the alopecia.
• Demodicosis. Hair plucks, tape strips, skin scrapings and biopsy will all be negative for mites.
• Hypothyroidism. This is the condition most easily confused with flank alopecia, especially at first presentation. However, flank alopecia cases are healthy with none of the accompanying signs associated with hypothyroidism, such as lethargy, poor exercise tolerance, thermophilia and the numerous associated biochemical and haematological abnormalities. Furthermore, thyroid function tests will be normal.
• Alopecia areata. Histopathological changes will differentiate.
• Topical steroid reaction. The history will suggest this unlikely cause for the signs seen.

Diagnosis

• The history and physical examination, especially with a repeated episode are typical, making the diagnosis straightforward in most cases.
• Rule out differential diagnoses if necessary.
• Histopathological examination. There are dystrophic, atrophic and keratin-filled hair follicles with finger-like projections into the dermis. Depending on the time of year there may be anagen follicles deeper in the dermis.

Clinical management

• Observation without treatment is appropriate in most cases as the problem is largely cosmetic.
• Melatonin implants have been used. In one report (Paradis, 1995) four Airedale terriers, four Boxers and one giant Schnauzer were all successfully treated.
• Some authorities (Miller and others, 2013; Hnilica, 2011) have reported success with oral melatonin at a dose between 3mg per day for dogs less than 25kg, and 6mg per day every 12-24 hours for three months once the disease has started, or for a similar time several weeks before the onset is expected as a preventive measure. Oral melatonin is inexpensive and obtainable in some countries, the United States for example, without a medical prescription. In the UK a prescription is required and the drug is not licensed for use in dogs.

References

1. Hnilica, K. A. Canine Recurrent Flank Alopecia (seasonal ank alopecia, cyclic ank alopecia, cyclic follicular dysplasia). In: Small Animal Dermatology. A Color Atlas and Therapeutic Guide. 3rd edition, pp 322-323. Elsevier, 2011.
2. Miller, W. H., Grif n, C. E. and Campbell, K. L. Canine Flank Alopecia. In: Muller and Kirk’s Small Animal Dermatology, 7th edition, pp 556-559. Elsevier, 2013.
3. Paradis, M. (1995) Canine recurrent flank alopecia: treatment with melatonin. Proc Am Academ Vet Dermatol Am Coll Vet Dermatol 11: 49.
4. Paradis, M. Melatonin therapy for canine alopecia. In: Bonagura, J. (ed) Current Veterinary Therapy X111, pp 546-549. WB Saunders, 2000.